Method and Apparatus For Geothermal Energy Recovery From Wellbores

ABSTRACT

Methods are disclosed for magnetically ranging and connecting a wellbore unto an opposing wellbore to create a continuous closed loop flow path from surface to downhole and back to surface again. The methods incorporate advanced directional drilling techniques, complex completion equipment as well as novel magnetic ranging systems which allow for the precise wellbore placement, zonal isolation and hydraulic communication required to recover geothermal energy by way of a circulated working fluid.

BACKGROUND Field of the Invention

The present disclosure relates to devices and methods for the installation of deep wellbores that form a loop subsurface and that connects two wellbores thereby creating a closed loop. The present disclosure discusses utilizing advanced directional drilling techniques along with complex completions downhole hardware and an implementation of novel magnetic ranging technology to create the closed loop subsurface architecture.

Background of the Invention

Geothermal wellbore drilling involves the installation of deep wellbores in wet and hot formations in the earth. Once accessed, these formations allow for the production of hot water and/or steam which is subsequentially used to produce electricity or district heating.

The traditional technique of geothermal energy harvesting requires that a formation of interest be both hot and contain movable water in order for the production technique be viable. This requirement constrains the application to a select few geographical locations and associated formations which satisfy the aforementioned reservoir properties. This fact limits the application of geothermal drilling to geographical locations which match the required criteria so as to allow for the economically justifiable capital expenditure required to produce energy at a rate and cost that is market competitive.

To address the lack of scalability and ubiquitousness of traditional geothermal techniques, several closed loop geothermal solutions have been reduced to practice and deployed. These solutions include but are not limited to drilling 3D wellbores with both vertical and horizontal sections that intersect and subsequentially make up a closed loop system through which a working fluid can be circulated. These systems have the advantage of being “contained” or “closed” in that they can be installed in a hot formation that is dry. In these scenarios, the working fluid in the closed loop is heated as it is pumped through the loop. Once on surface, the heat can be stripped from the working fluid by suitable commercially viable heat exchanger units, and the cool fluid can be reinjected into the flow loop and delivered to hot formation on a subsequent round of circulation through the system.

A drawback of current techniques for creating closed loop systems is that it requires that a relative downhole measurement of proximity between wellbores be deployed so that wellbores can be guided to connect with one another. Traditionally, this requires deploying a magnetic field source or receiver in one of the wellbores and then guiding the adjacent wellbore with said receiver/source so that wellbores be connected and the closed loop formed. The process of deploying the magnetic ranging system as described requires two drilling rigs and other hardware. Typically, one of the wellbores which will make up the pair that is to be connected will be drilled. The drill string is withdrawn, and a magnetic sensor or source is deployed in the drilled well. As the second well is drilled, the device deployed in the previously drilled wellbore allows for the guidance and eventual connection between wells. This process is commonly referred to as magnetic ranging, and well-known commercial system exist to allow for this. However, the costs associated with these operations become prohibitive and drive the projects economics in an unfavorable direction, as a drilling rig is usually required to deploy and position the magnetic ranging device in close proximity to the wellbore being drilled.

The present inventions seek to overcome the aforementioned shortcomings discussed above. This is accomplished by the present disclosure, the novel method of wellbore placement and novel hardware required to intersect and complete a new type of closed loop circulation system for geothermal energy production.

SUMMARY OF THE INVENTION

A section of wellbore is drilled down to the formation of interest. A casing is typically installed at this point, but it need not be if overburden collapse is not a concern given the set of formations comprising the overburden of rock. For the sake of discussion and the purposes of this application, the wellbore in question will be deviated from vertical to horizontal by way of directional drilling, although someone familiar with or skilled in the art will realize that the subject invention need not be limited to this particular geometry.

As the well is drilled to greater total depths, the three-dimensional position of the drilling bit becomes more and more uncertain due to cumulative and compounding errors associated with standard wellbore surveying techniques. These errors in position will be of the order of magnitude such that closing the loop via well intersection will be impossible without a form of relative downhole range finding, otherwise referred to in industry as “magnetic ranging”.

The magnetic ranging techniques that are typically used in commercial and pre-commercial closed loop techniques typically require access to the adjacent well as a source or receiver deployed in the adjacent wellbore that is to be intersected in order for the technique to be viable. In several embodiments of the present invention discussed below, the deployment of instruments in an additional well is not needed as the drilling well assembly will act as the source and receiver for the novel magnetic ranging system that is being disclosed.

In one embodiment, instead of having a single bore, multiple wellbores can be drilled and connected using similar ranging measurement techniques. In this embodiment, a section of wellbore is drilled down to the formation of interest. A casing is typically installed at this point. For the sake of discussion and the purposes of this application, the wellbore in question will have been deviated from vertical to horizontal by way of directional drilling, although someone familiar with or skilled in the art will realize that the subject invention need not be limited to this particular geometry. As the first well is drilled, a second offset or “twin” of the well profile of the first well is also drilled and a casing is set. FIG. 1 shows the two wellbores which have been deviated to 90° and are stacked one “on top” of the other. Drill out of both intermediate casing shoes can occur at the same time via two separate rigs, or a rig with a double derrick. Both drillstrings may have subs in which rare earth magnets (or other suitable magnetic signal mechanisms) are installed transverse to the long axis of the drill string. As the drill strings rotate, an elliptical magnetic field with temporal characteristics is created about each drill string. The frequency of rotation in rotations per minute of the respective drill strings will dictate the frequency at which the magnetic fields from the rare earth magnets rotate.

The rotating magnetic fields of each drill string can be sampled by an onboard measurement with drilling sensor integral and separately installed magnetometer package in the adjacent drill string. The RPM of a particular drill string can be adjusted so as not to conflate the measurement and signal analysis of the upper string with that of the lower string.

As drilling continues, distance and direction between wellbores from a reference point in each wellbore can be calculated. These relative proximity measurements can then be used to adjust the trajectory of one or both wellbores to keep the two wellbores optimally aligned as a pair, and eventually to guide one or both wellbores to intersect the other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical section view of two wells that are drilled and that can be connected to create a closed loop system.

FIG. 2 illustrates the two well system and ranging techniques that can be used to connect the two wells to create a closed loop system.

FIG. 3 illustrates the two well system and ranging techniques that can be used to connect the two wells to create a closed loop system.

FIG. 4 illustrates how ranging techniques can be used to connect the two wells.

FIG. 5 illustrates a closed loop flow path single well and associated heat exchange equipment that can be used to recover geothermal energy.

FIG. 6A illustrates an example of a single communication path in a drill pipe with an insulating material on one side that can be used as a wired communication path.

FIG. 6B is an example of two communication paths in a drill pipe with insulating material surrounding the communication paths that can be used as multiple wired communication paths.

FIG. 6C is an example of a connector that can be used to connect the communication paths of sections of drill pipe.

DETAILED DESCRIPTION

The present disclosure relates to systems and methods for creating a closed loop system to recover geothermal energy from geothermal wells. Further, a system and method are disclosed that includes drilling two wells and using ranging techniques to connect the two wellbores at a desired location to create a closed loop system.

In one embodiment, magnetic field sensors are contained in a sub between a drill bit and the drive train of a mud motor. This arrangement allows for the magnetometers contained in the sub to rotate at a different frequency than the tail of the drill string. This difference in rotation allows temporal signal analysis techniques to be utilized in the computation of the ranging measurement, as the rotating magnet source has a unique frequency of rotation as compared to the magnetometer package.

In yet another novel approach, industry standard MWD sensors can be used to collect magnetic field measurements as the sensor passes by the adjacent magnetic field source in the tail section of the drilling assembly. These data can once again be processed downhole or transmitted to surface so that a ranging measurement is made available.

Another alternative embodiment for creating a geothermal closed loop well is illustrated in FIG. 1 . As the first well is drilled, a second offset or “twin” of the well profile of the first well is also drilled and a casing is set. FIG. 1 shows the two wellbores which have been deviated to 90° and are stacked one “on top” of the other. Drill out of both intermediate casing shoe can occur at the same time via two separate rigs, or a rig with a double derrick. As shown in FIG. 2 , both drill strings may have subs, 201 and 202, in which rare earth magnets (or other suitable magnetic signal mechanisms) are installed transverse to the long axis of the drill string. As the drill strings rotate, an elliptical magnetic field 203 with temporal characteristics is created about each drill string. The frequency of rotation in rotations per minute of the respective drill strings will dictate the frequency at which the magnetic fields from the rare earth magnets rotate.

The rotating magnetic fields of each drill string can be sampled by an onboard measurement with drilling sensor integral and separately installed magnetometer package in the adjacent drill string. The RPM of a particular drill string can be adjusted so as not to conflate the measurement and signal analysis of the upper string with that of the lower string.

As illustrated in FIG. 3 , additional subs 301 can be placed serially along the drill string to protect against a case where the measure depth of each well are not the same.

As drilling continues, distance and direction between wellbores from a reference point in each wellbore can be calculated. These relative proximity measurements can then be used to adjust the trajectory of one or both wellbores to keep the two wellbores optimally aligned as a pair, and eventually to guide one or both wellbores to intersect the other.

FIG. 5 shows a completed geothermal well, including heat exchange equipment 501 that can be used at the surface to recover the geothermal energy produced from the well. As will be understood by one of skill in the art, in addition to the production of hot fluid coming from the well annulus as shown, it could come from other alternatives as described herein, including a tubing string, casing string, or any other known means, and further could be connected to the as shown heat exchange mechanism using known techniques.

The multiple drill pipes which will make up sections of the long drill string can contain at least one wired communication path that can be connected between sections of drill pipe to provide for data and other communication from downhole points in the well bore to the surface. Examples of wired communication paths include telephone lines, ethernet cables, other known cable lines, metal wire conductors, braided ribbon, and fiber-optic lines. Other known communication wires known to those skilled in the art can also be used. The isolation for this communication element can provide insulation from the drill pipe body itself, along with the electrically conductive fluid that will be pumped down the drill pipes. One solution for this has been described in application US20190119990, where a radially expansive conductive element is used to line the interior of an industry standard drill pipe. This conductive member is both insulated from the ID of the drill pipe and the drilling fluid being pumped down the drill pipe by an electrically insulative epoxy coating. However, the conductive member may also be insulated from the drill pipe by any conventional method known by one of skill in the art, one example being an epoxy coated drill pipe containing a conductive element that is insulated from the body of the drill pipe but is not insulated from the fluid pumped down the drill pipe. In some embodiments of the inventions disclosed herein a section or all of the ID of a commercial pipe is coated with a nonconductive material such as epoxy, and then one or more ribbons of insulated wire (or other form of wired communication) is positioned in the epoxy layer as show in FIGS. 6A-6C.

FIG. 6A shows a section of drill string coated on its inner diameter with an insulating material such as epoxy 601. A wired communication mechanism, 602, such as an insulated or uninsulated ribbon, a braided wire, an impregnated material, a telephone wire, an ethernet cable, a fiber-optic cable, or any suitable wired communication line is located in close proximity to, or embedded into, the insulating material. FIG. 6B shows an example of two separate wired communication mechanisms, 603 and 604. Each wired communication mechanism can land on either side of the drill pipe, or each communication mechanism can be stepped so as to allow for separate “channels” of communication to be dedicated to each communication mechanism. This allows for additional configurations of communication to the surface and return communication paths. FIG. 6C shows an example of a mechanism for connecting the wired communication mechanisms as described. In this example, the two separate communication mechanisms are connected using a step connection. One communication mechanism is contacted using a smaller diameter ring 606 and the second communication mechanism is connected using a larger ring 607. The ring assures contact from box to pin of the drill pipes when joints of pipe are added to the drill stem. As will be appreciated by one of skill in the art, there are multiple manners in which to contact/connect the communication mechanisms of each segment of drill pipe while isolating each communication mechanism, thus providing multiple paths for communication between surface and points in the well bore down hole.

Another embodiment involves a three-step coating process that layers nonconductive coatings and communication mechanisms inside a common piece of pipe. Firstly, a non-conductive epoxy is coated inside the ID of the pipe. Next, the communication mechanism or mechanisms is/are installed on or into the epoxy. Finally, an additional layer of non-conductive epoxy (or similar insulating material) is installed. This has the effect of protecting the inner conductive layer from electrical contact with both the drill pipe and the drill pipe fluids, all while providing one or more wired communication paths for communication between downhole and the surface.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. 

What is claimed is:
 1. An apparatus for connecting two wellbores comprising: a first drill string; the first drill string having a bit; the first drill string having a magnet that is capable of generating a magnetic field when rotated; the first drill string having a magnetic field sensor; a second drill string; the second drill string having a second bit; the second drill string having a magnet that is capable of generating a magnetic field when rotated; the second drill string having a magnetic field sensor.
 2. The apparatus of claim 1 wherein the first drill string further comprises at least two magnets that are each capable of generating a magnetic field when rotated.
 3. The apparatus of claim 1 wherein the second drill string further comprises at least two magnets that are each capable of generating a magnetic field when rotated.
 4. The apparatus of claim 1 wherein the magnetic field sensor in the first drill string is installed between the drill bit and a drive train of a mud motor.
 5. The apparatus of claim 1 wherein the magnetic field sensor in the second drill string is installed between the drill bit and a drive train of a mud motor.
 6. The apparatus of claim 1 wherein the magnet in the first drill string is a rare earth magnet.
 7. The apparatus of claim 1 wherein the magnet in the second drill string is a rare earth magnet.
 8. The apparatus of claim 1 wherein the first drill string and the second drill string are capable of rotating at different speeds.
 9. An apparatus for connecting two wellbores comprising: a first drill string; the first drill string having a mechanism capable of generating a magnetic field; the first drill string having a magnetic field sensor; a second drill string; the second drill string having a mechanism capable of generating a magnetic field; the second drill string having a magnetic field sensor.
 10. The apparatus of claim 9 wherein the first drill string further comprises at least two mechanisms that are each capable of generating a magnetic field.
 11. The apparatus of claim 9 wherein the second drill string further comprises at least two mechanisms that are each capable of generating a magnetic field.
 12. The apparatus of claim 9 wherein the mechanism capable of generating a magnetic field in the first drill string is between a drill bit and a drive train of a mud motor or the steering head of rotatable steering assembly, or the drive train of a turbine.
 13. The apparatus of claim 9 wherein the mechanism in the first drill string is a magnet.
 14. The apparatus of claim 9 wherein the mechanism in the second drill string is a magnet.
 15. A method of connecting two well bores comprising: installing a drill string containing a mechanism that generates a magnetic field when rotated in a first wellbore; installing a magnetic field sensor in the first wellbore; installing a drill string containing a mechanism that generates a magnetic field when rotated in a second wellbore; installing a magnetic field sensor in the second wellbore; rotating the first drill sting; sensing the magnetic field produced; adjusting drilling operations of the first drill string to alter a characteristic of the drilling operations.
 16. The method of claim 15 further comprising: rotating the second drill string; sensing the magnetic field produced from the mechanism in the second drill string; adjusting drilling operations of the second drill string to alter a characteristic of the drilling operations.
 17. The method of claim 16 wherein the second drill string is rotated at a different speed than the first drill string.
 18. The method of claim 16 wherein the characteristic of drilling operation is adjusted such that the angle of drilling is changed. 